Turkey's objections to Sweden and Finland joining the NATO alliance persist despite diplomatic efforts and are not likely to change until the two Nordic countries refrain from supporting anti-Turkey groups, experts said.

Sweden and Finland formally applied to join the North Atlantic Treaty Organization (NATO) last week following the Russia-Ukraine conflict erupted in February.

NATO allies, except for Turkey, have welcomed the Nordics' appeal. Turkey, however, citing the Swedish and Finnish ties with the Kurdistan Workers' Party (PKK) and other anti-Turkey terrorist groups, objected to their entry into the alliance.

Turkey demanded an array of "concrete assurances" from Sweden and Finland earlier this week, including "termination of political support for terrorism", "elimination of the source of terrorism financing" and "cessation of arms support" to the outlawed PKK and a Syrian Kurdish offshoot.

The demands also called for the lifting of arms sanctions against Turkey and global cooperation against terrorism.

Accession of new member states requires consensus among existing NATO members, and that is where Ankara comes in.

Analysts insist that the Finnish and Swedish approach to the PKK remains key for Turkey's government.

"The threat of a Turkish veto is real unless the two Scandinavian states cut in some way their ties with Kurdish groups deemed terrorist by Ankara. This is not a bargain but a firm Turkish demand," Turkish foreign policy analyst Serkan Demirtas said.

Ankara has issues with Sweden because Turkish Kurds are a noticeable political presence in the country, and to a lesser extent with Finland, which also supports Kurdish groups, said Demirtas, also the Ankara bureau chief of Turkish Daily News.

Turkey feels that Sweden and Finland have been insensitive to its demands to change their stance on issues that are relevant to Turkey's national security, Demirtas argued.